1. Field of the Invention
The present invention relates generally to barrier cable anchorage systems and, more particularly, to a system and method for ensuring proper barrier cable anchorage positioning.
2. Description of the Background
Building codes require parking structures, like all structures, to provide fall protection for occupants where vertical drops between ramps or elsewhere within the space exceed an allowable minimum, typically 12 or 30 inches. Fall protection in garage structures commonly takes the form of a barrier system such as a railing located along exterior structure edges as well as at the edges of the numerous interior ramps and grade changes within the structure that allow vehicles to access the space. Fall protection barriers provided only for pedestrian safety are not expected to experience high loading conditions and can thus be relatively lightweight. Significantly greater loads are anticipated in areas of vehicular traffic and barrier system must be engineered to resist those loads.
Acceptable vehicular barrier systems can be provided by reinforced concrete or masonry walls, although these systems are relatively expensive and heavy. The added weight may impact the overall design of the structure itself. Steel cable barrier systems are lighter, provide visibility inside the structure for vehicle safety, and are less expensive and are consequently perhaps the most commonly used vehicular and pedestrian barrier system in parking structures. Barrier cable systems typically use ½ inch diameter, 7-wire steel strands that are galvanized for corrosion resistance, and sometimes plastic (polyethylene) or epoxy coated for aesthetic reasons. Barrier cable systems designed for passenger car vehicular traffic, and indeed passenger vehicle barriers of all types, must be designed to resist a single 6,000 pound load applied horizontally in any direction. For design purposes, the load is presumed to be applied at a minimum height of 18 inches above the finished floor surface over an area not exceeding one square foot and cable deflection under load should not exceed 18-inches. Multiple steel barrier cables are readily able to handle such loads. Consequently, failure of a cable barrier system is most likely to occur at the cable anchorages or at the connection between the anchorages and the supporting structure, typically the concrete columns or other elements of the garage structure.
A variety of surface mounted and embedded methods are used to anchor the cable ends to the concrete structure of the garage. In a typical anchorage assembly, each cable of the barrier passes through the column and into a pocket on the opposite side in which an embedded wedge type anchor was situated before the column was cast. The cable passes through the conically tapered barrel of the anchor into which a series of wedges are positioned around the cable. As the cable is tensioned by pulling it through the column using a tensioning jack, the cable elongates and the wedges permit the cable to pass though the barrel. However, when the tensioning jack is released the cable recoils and the wedges clamp down on the cable as it is drawn into the tapered barrel, thereby maintaining cable tension. The cable may be anchored in this manner where access to the opposite side of one or both of the end columns is accessible. Where no access is available to the opposite side of a column the cable may be anchored at one end at the face of the column and tensioned at the other end as described. With reference to FIGS. 1 and 2, face anchoring of cables where backside access is limited may be accomplished by individually placing a female threaded ferrule loop insert within the column formwork for each cable. A temporary bolt may be inserted into the threaded loop insert to protect the threads. After the concrete has cured the temporary bolt is removed and a cooperatively threaded male cable connector is advanced into the female insert. The male “Fixed-End Grabb-It®” type connector uses a conical barrel and wedge system to anchor the cable as illustrated and described above. Similarly, if there is no access to the opposite side of both end columns, a face mounted solution can be utilized at both locations where one end used a “Fixed-End Grabb-It®” and the opposite end uses a “Stress-End Grabb-It®”
With both through and face anchored cables, it is necessary to accurately and securely position the anchorage for each of the barrier cables before pouring the concrete structure because, even though vehicular loading governs most aspect of barrier design, pedestrian barrier cable spacing is dictated by building codes that limit the size of any opening through the barrier for the protection of children. Cable openings are limited to being smaller than will allow a four inch sphere to pass through. In practice this typically means that cables are placed on 4-inch centers such that the space between would be 3½-inches. Accurately positioning individual anchors within the concrete formwork for each of the cable strands needed to meet the 42-inch minimum pedestrian barrier height on 4-inch centers is critical and consequently time consuming and costly. Even a slight misalignment of an anchor can result in the barrier cable failing to meet the maximum space limitation of the building code and requiring additional, costly remedial work by the contractor to correct the error after the concrete structure has been erected.